Third party suppliers give you all the info you need up front: fixed or variable rate and whether or not there is a fee for canceling or changing the supplier before the contract is done. For example I am using a company based out of AZ I have a three year contract with for 7.9c per kwh that ends in October of next year. At that point I'd pay whatever fee they currently charge unless I switch to a different supplier. I face no fees if I change suppliers before then. The big thing I'd say look out for are places with really low fees but short contract times such as 6 months because it is easy to forget to change your supplier. I tend to set phone reminders the month before my contract ends so I can look for the next best deal if my current supplier rate is set to spike after the contract ends. I imagine some places are so much lower is based on where they are located and how they generate or supplement generation of electricity. Like my company is in AZ so maybe it makes sense for them to sell electricity to a heavily populated state like ours where people desperately want cheaper per kwh rates.

I have used third party providers exclusively since CT has allowed them and have never been hit with any hidden fees or surprises since I read all conditions in each contract before signing on.